The Alzheimer's Clinical Trial Consortium ? Down Syndrome Network (ACTC- DSN) Principal Investigators: Paul Aisen, Reisa Sperling, Ron Petersen Co-Investigator: Michael Rafii This application is being submitted to PA-18-591 in accordance with NOT-OD-18-194. ABSTRACT With this supplement, we request funding to utilize the existing depth and breadth of expertise across the Alzheimer's Clinical Trial Consortium (ACTC) infrastructure to conduct Alzheimer's Disease (AD) clinical trials in adults with Down syndrome (DS). The overarching goal of this proposal is to build an efficient clinical trial network to address the critical need for treatment of AD in adults with DS, the world's largest genetically defined population with AD. There is currently no network in place to conduct clinical trials in this at-risk population. It is our view that such a network can be created effectively through the ACTC and through our existing close collaboration with the Alzheimer's Biomarker Consortium in Down syndrome (ABC-DS).